The wet milling of corn in the United States of America produces over 4 million tons of corn fiber each year. To date, this corn fiber has been used in animal feed applications, at least in the United States. Corn fiber comprises, among other things, arabinoxylan, which is also referred to as hemicellulose and corn fiber gum. Arabinoxylan derived from corn potentially has commercial value far exceeding its use in animal feed applications. For example, it is believed that corn arabinoxylan may be used as a replacement for gum arabic in applications such as beverage flavor emulsification. Additionally, it is believed that corn arabinoxylan may be useful in applications such as film formation, thickening, emulsification, and stabilization of aqueous solutions and suspensions. Further, it is known that including corn arabinoxylan and its limited hydrolysis products, the arabinoxylan oligosaccharides (AXOS), in foods and beverages may yield health benefits such as increased absorption of calcium and magnesium, reduced cholesterol absorption, lowered plasma cholesterol, decrease cholesterol accumulation in the liver, and desirable bifidogenic effects.
In view of the number of possible relatively high value applications for corn arabinoxylan, it is no surprise that processes for extracting arabinoxylan (and arabinoxylan oligosaccharides in particular) from corn fiber on a commercial scale have been and continue to be the subject of investigation and development activities.
Arabinoxylan is an polysaccharide having a backbone repeat unit of [β-(1,4)-D-xylopyranose]. Partial hydrolysis of arabinoxylans can yield arabinoxylan oligosaccharides, which are sometimes referred to by the acronym “AXOS.” The arabinoxylan backbone is substituted with, inter alia, arabinose side chains, with a portion of the arabinose side chains being esterified with phenolic compounds, in particular phenolic acids such as coumaric acid and ferulic acid (e.g., one or two phenolic acid moieties may substituted on a single xylose repeat unit of the backbone). Ferulic acid is an aromatic compound with potent antioxidant activity and known human health benefits. Other phenolic acids present in bound form in arabinoxylan such as coumaric acid are also believed to have activity as antioxidants. It would be desirable to develop efficient methods for generating AXOS from corn fiber which leave the ferulic acid and other phenolic substituents on the AXOS backbone largely intact, i.e., still chemically bound to the oligosaccharide. The bound ferulic acid residues in the AXOS could provide sustained release of antioxidants during digestion of the AXOS in the digestive tract following consumption of an article such as a food product containing the AXOS. The arabinoxylan polysaccharides in corn fiber are tough, gummy, high molecular weight substances that are covalently crosslinked (through the ferulic acid ester substituents) both to themselves and to lignin structures in the corn fiber. Extracting arabinoxylan oligomers in soluble form from the corn fiber generally involves a cleavage of the covalent bonds involved in such crosslinking. However, previously developed methods for the extraction of arabinoxylan oligomers under alkaline conditions have tended to also cleave the ferulic acid esters substituted on the arabinose side chains of the polysaccharide backbone. Such methods thus result in the loss of a substantial fraction of the bound ferulic acid. Additionally, alkaline extraction is not very effective and introduces salts and color into the extract which are difficult to remove. Acid treatment methods for extracting arabinoxylan oligomers from corn fiber are also known, but such methods significantly degrade the arabinoxylan oligosaccharides and therefore require close control of the process parameters (e.g., amounts of acid and corn fiber, temperature). Such methods also often generate relatively large amounts of mono- and disaccharides, thereby reducing the yield of the desired arabinoxylan oligosaccharides. The residual acid in the extract also must be neutralized, generating salts which typically must be removed to make the extract suitable for use as a food grade ingredient.